A glucanase-driven fractionation allows redefinition of Schizosaccharomyces pombe cell wall composition and structure: assignment of diglucan

Purified endoglucanases have been used to determine the composition of Schizosaccharomyces pombe cell wall. This structure has been traditionally studied after isolating its components (mannoproteins, alpha1,3-glucan, beta1,3-glucan, and a branched beta-glucan) with hot alkali. Instead, we sequentially removed the polysaccharides by digesting with endo-beta1,3-glucanase and with a novel endo-alpha1,3-glucanase (mutanase). After this gentle isolation we observed that a branched beta1,3-beta1,6-glucan is much more abundant than previously described. By scaling-up the new protocol we prepared large amounts of the highly branched glucan and determined its structural features. We have named this highly branched beta-glucan diglucan, reflecting its two types of beta linkages. We have also identified an insoluble endoglucanase-resistant type of 1,3-linked glucan present in S. pombe cell walls. We redefined the wall composition of S. pombe vegetative cells by this new method. Finally, to demonstrate its application, we determined the cell wall composition of known mutant strains.